Method of protecting the surface of a substrate

ABSTRACT

The surface of a metallic base system is initially coated with a metallic alloy layer that is ductile and oxidation resistant. An aluminide coating is then applied to the metallic alloy layer. The chemistry of the metallic alloy layer is such that the oxidation resistance of the subsequently aluminized outermost layer is not seriously degraded.

United States Patent [191 Gedwill et al.

[451 Nov. 26, 1974 METHOD OF PROTECTING THE SURFACE OF A SUBSTRATE [75]Inventors: Michael A. Gedwill, Lakewood;

Salvatore J. Grisaffe, Rocky River, both of Ohio [22] Filed: Oct. 16,1972 [21] Appl. No.: 298,156

[52] US. Cl 29/460, 29/196.6, 29/197, 29/494, 29/497.5, 29/504 [51] Int.Cl B23p 3/00, B23p 19/04 [58] Field of Search 29/196.6, 197, 504, 494,

[56] References Cited UNITED STATES PATENTS 2,473,712 6/1949 Kinney 29/1966 X Sayre 29/494 X 3,367,022 2/1968 Hill i 29/504 X 3,647,5173/1972 Milidantrl 29/l96.6 X

3,649,225 3/1972 Simmons 29/196.6 X 3,676,085 7/1972 Evans et al. 29/197X Primary ExaminerChar1ie T. Moon Attorney, Agent, 'or Firm-G. E. Shook;N. T. Musial; J. R. Manning 5 7 ABSTRACT The surface of a metallic basesystem is initially coated with a metallic alloy layer that is ductileand oxidation resistant. An aluminide coating is then ap plied to themetallic alloy layer. The chemistry of the metallic alloy layer is suchthat the oxidation resistance of the subsequently aluminized outermostlayer is not seriously degraded.

10 Claims, No Drawings METHOD OF PROTECTING THE SURFACE OF A SUBSTRATEORIGIN OF THE INVENTION The invention described herein was made byemployees of the United States Government and may be manufactured andused by or for the Government for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION fluence on coating chemistry, thickness, andproperties. Thus, it is difficult to tailor an aluminide coating toresist a particular engine environment. As engine temperatures increaseto improve performance, aluminide conversion coatings alone offer lesspotential for providing long time oxidation and thermal fatigueresistance.

Nickel and cobalt base superalloys and dispersionstrengthened alloys areused as turbine vanes and blades in aircraft and land-based gas turbineengines. Oxidation, hot corrosion, and thermal fatigue cracking aremajor factors which limit the useful life of these ma-- terials.Aluminide coatings are used to extend the life of these superalloys byproviding a more oxidation and hot corrosion resistant surface in whichthermal fatigue cracking is reduced.

The aluminide coatings are in themselves made of a hard, brittleouter-layer and a hard, brittle multiphase sub-layer that can crackunder high thermal stresses. Once cracked, the oxidizing and/or hotcorrosion environment has direct access to the underlying substrate, anddeleterious attacks can occur. Also certain elements in the superalloysubstrate enter into these coatings. This generally reduces theenvironmental resistance of the coatings and makes them less ductile.

SUMMARY OF THE INVENTION According to the present invention thesubstrate is initially overlayed with a ductile, oxidation resistantmetallic alloy layer. This overlay is achieved by foil cladding or othermeans, such as physical vapor deposition, ion plating, sputtering,plasma spraying, or slurry sintering. Foil cladding requires morepreliminary effort and fixturing, but it supplies a well characterizedhomogeneous material directly on the superalloy. Thus Thus, a failsafesystem is provided. The aluminide outer layer has a tendency to be lessembrittled by substrate elements. It has a lessened tendency to crackbecause it is supported by a ductile layer, not a brittle, multiphaselayer that is conventionally the case. If a crack occurs in thealuminide outer-layer, the ductility of the underlayer restricts itspropagation. Widespread oxida tion of the underlayer does not occurbecause the metallic underlayer is oxidation resistant.

OBJECTS OF THE INVENTION It is, therefore, an object of the presentinvention to provide an improved oxidation resistant coating forsuperalloys and dispersion-strengthened alloys.

Another object of the invention is to provide an aluminized coatinghaving long time oxidation and thermal fatigue resistance for thesematerials.

A further object of the invention is to provide an im proved aluminizedcoating for nickel base and cobalt base superalloys,dispersion-strengthened alloys, composites, and directional eutectics.

These and other objects of the invention will be apparent from thespecification which follows.

PREFERRED EMBODIMENT OF THE INVENTION According to the present inventiona ductile, oxidation resistant metallic alloy is initially applied tothe superalloy. An aluminide coating is then applied to the metallicalloy.

In order to illustrate the beneficial technical effects of the inventionNiCrAlSi and FeCrAlY foil claddings were applied to typical nickel andcobalt base superalloys of the type used in gas turbine engines. Thenominal composition of the first mentioned cladding was 15 to 25 percentchromium, 3' to 6 percent aluminum, 0.5

'to 1.5 percent silicon, and the remainder nickel. The

preferred composition was 18 percent chromium, 4 percent aluminum, 1percent-silicon, and the remainder nickel.

The other cladding had a nominal composition of 15 to 25 percentchromium, 3 to 6 percent aluminum, 0.1

. to 1 percent yttrium, and the remainder iron. The preferredcomposition was 25 percent chromium, 4 percent aluminum, l percentyttrium, and the remainder iron.

These claddings were applied to nickel base superalloys known as IN-l00and WI-52. The nominal composition of the [N alloy was.15 percentcobalt, 9.5 percent chromium, 5.3 percent aluminum, 4.3 percenttitanium, 3.2 percent molybdenum and the remainder nickel. The nominalcomposition of the Wl-52 was 21 percent chromium, 11 percent tungsten,2.2 percent iron, 1.9 percent columbium, 0.9 percent silicon and theremainder cobalt. The claddings were also applied to WAZ-20 and NX-188advanced superalloys and to The chemistry of the overlay coating is suchthat the oxidation resistance of the subsequently aluminized outermostlayer is not seriously degraded. The aluminide outer layer can bedeveloped by pack cementa- TD-NiCr dispersion-strengthened alloy. Thenominal compositions were, for WAZ-ZO, 20 percent tungsten, 6.5 percentaluminum, 1.5 percent zirconium, 0.2 percent carbon and the remaindernickel; for NX-l88, 18 percent molybdenum, 8 percent aluminum, 0.04percent carbon and the remainder nickel; and for TD-.

NiCr, 20 percent chromium, 2 percent thorium dioxide, and the remaindernickel. It is further contemplated that the substrate can be nickel andcobalt base composites and directional eutectic alloys.

Claddings having a thickness of 0.127 millimeter of both materials wereapplied to the substrate specimens by hot isostatic gas pressure bondingat a helium pressure of 15,000 to 20,000 psi for 2 hours at I090C.Aluminide coatings were then applied to the claddings by packcementation at l,900 to 2,000F in argon using a powder mixtureconsisting of 1 percent sodium or amonium halide, 1 percent aluminum,and the remainder aluminum oxide. It is also contemplated that thealuminide coating can be applied by a sintered or fused slurry,electrodeposition, physical vapor deposition, ion plating, sputtering,hot dipping, or pyrolysis. The electrodeposition can be of the aqueous,fused salt, or electrophoresis type. The spraying can be either a flameor plasma type.

The system performance was primarily evaluated on the basis of weightchange, visual appearance, and metallographic change. Weight changeresults of furnace tests on NiCrAlSi clad IN-100 and WI52 at l,090C for20 hour exposure cycles were obtained. These tests showed that theclad-cladding alloy was oxidation resistant in that it gained weight informing a protective oxide and then little further weight changeoccurred. While NiCrAlSi clad on IN-l showed a slight turnaroundprimarily due to spalling, it was more protective than on WI52. Bothbare lN-IOO and bare WI-52 lost weight rapidly. Exposure at 1,040Cresulted in more protective behavior for both cladding systems for timesup to 400 hours.

Metallographic cross sections of the NiCrAlSi cladding on IN-l00 showedthis system was relatively unef fected by 200 hour cyclic furnaceoxidation at l,090C. NiCrAlSi clad WI-52 showed considerable surfaceoxide penetration and internal oxidation in the cladding after only 120hours of tests.

The FeCrAlY cladding was evaluated in cyclic furnace oxidation on IN-IOOand WI-52. The l,090C weight change behavior of the clad WI-52 wasalmost identical to that of the cladding alloy itself. The clad IN-lOO,however, showed more rapid weight gains accompanied by significantspalling. A lower exposure temperature of l,O40C resulted in lessoxidation attack for the claddings on both substrates.

Metallographic and weight change data obtained after l,090C furnacetests on the commercial aluminide coatings were compared with similardata with the most protective claddings on each substrate. Thesecomparisons indicated that both the attack on the microstructure andweight changes of the coating and Ni- CrAlSi cladding on IN-IOO werevery similar after 200 hours hour cycles) at l,090C/Here, bothprotection systems were approximately the same thickness. The FeCrAlYcladding on WI-b 52 was in much better condition than the completelydegraded coating, but it was about twice as thick in the as-cladcondition. This ease in controlling thickness is a beneficial technicaleffect of the overlay or cladding process.

The most promising cladding systems based on furnace testing were theNiCrAlSi clad IN-lOO and the FeCrAlY clad WI-52; FeCrAlY clad IN-IOOalso appeared to have some 'potential. These systems were subjected toMach 1 burner rig testing at both I,040 and l,090C using 1 hour exposurecycles followed by air blast quenching. Such testing imposedsignificantly greater thermal stress on the protection system and thesurface oxide, especially at the leading edges of the burner rigspecimens. The FeCrAlY cladding perfortned better on both IN-IOO andWI-52 than did the NiCrAlSi cladding. The thermal fatigue resistance ofthese clad systems was markedly superior to that of the aluminide coatedsystems. In all tests, no cracks were observed in the claddings withinthe test times. Only the FeCrAlY clad WI-52 performed better inoxidation erosion than the aluminide coating.

Some NiCrAlSi clad IN-IOO burner specimens were aluminized to obtain thebenefits of both protective systems. Soft ductile claddings had shownsuperior resistance to thermal fatigue cracking while harder and morebrittle aluminide coatings resisted oxidation better. Aluminizing theNiCrAlSi claddings produced a markedly improved protection system forlN-l00. The system withstood at least 800 hours of Mach 1 burner rigtesting at l,090C. Based on the time to show weight change turnaround,the aluminized cladding was four to five times as protective as thecommercial aluminide coating. Its thermal fatigue resistance was aboutthree times better than the aluminide coating.

The primary cause for improvement in thermal fatigue resistance isbelieved to be the existence of a rather ductile oxidation resistantlayer of aluminum enriched cladding under the external aluminidecoating.

In conventional aluminide coatings on superalloys, a hard, carbide richzone is typically found here. Benefits may also be derived from theconversion of the relatively simple NiCrAlSi alloy to the aluminide.This aluminide would be expected to contain little of the strengtheningelements found in the IN-l00.

Several aluminized NiCrAlSi clad WAZ-ZO, NX-l 88, and TD-NiCr specimenswere tested in cyclic furnace oxidation at 1,l50C to see how effectivethe coating would be for higher temperature applications. The oxidationlife of the clad was well in excess of 500 and 300 hours, respectively,on WAZ-ZO and NX-l 88, and slightly more than 600 hours on TD-NiCr. Asubstantial improvement over aluminide coatings alone on thesesubstrates which generally failed well within hours in the same tests.

Burner rig tests at l,090C and Mach-l were conducted on aluminized,electron beam melted and physical vapor deposited NiCrAlSi coatings onIN-l00 and NASA-TRW Vl-A. The nominal composition on the coatingsas-deposited is 15 percent chromium, 4 percent aluminum, 1 percentsilicon, and the remainder nickel. The nominal composition of NASATRW-Vl-A superalloy is 7.5 percent cobalt, 6.0 percent chromium, 5.8percent tungsten, 5.4 percent aluminum, 9.0 percent tantalum, 2.0percent molybdenum, l.0 percent titanium, 0.5 percent columbium, 0.40percent rhenium, 0.5 percent hafnium, 0.1 percent zirconium, O. I 3percent carbon, 0.015 percent boron, and the remainder nickel. Afterhours of testing in the very severe environment, the specimens showed noevidence of thermal fatigue cracking and the coating had completelyprotected the superalloy substrates from oxidation and erosion.

While several preferred embodiments of the invention have been describedit is contemplated that various modifications may be made withoutdeparting from the spirit of the invention or the scope of the subjoinedclaims. By way of example, claddings of NiCrAl containing one or more ofSi, Y, Mn and Th can be used. Also claddings of FeCrAl containing one ormore of Y, Si, Mn and Ta can be used.

What is claimed is:

1. A method of protecting the surface of a substrate of a metallic basesystem selected from the group consisting of nickel and cobaltcomprising the steps of cladding said surface with a ductile, oxidationresistant metallic alloy foil, and

aluminizing the outermost surface portion of said foil thereby formingan outer aluminide coating thereon.

2. A method of protecting the surface of a substrate as claimed in claim1 wherein the substrate comprises a nickel-base material selected fromthe group consisting of superalloys, dispersion-strengthened alloys,composites, and directional eutectic alloys.

3. A method of protecting the surface of a substrate as claimed in claim1 wherein the substrate comprises a cobalt-base material selected fromthe group consisting of superalloys, dispersion-strengthened alloys,composites, and directional eutectic alloys.

4. A method of protecting the surface of a substrate as claimed in claim1 wherein the substrate is clad with a NiCrAlSi metallic alloy foilhaving a nominal compo- V sition of about 18 percent chromium, about 4percent aluminum, about 1 percent silicon and the remainder nickel.

6. A method of protecting the surface of a substrate as claimed in claim1 wherein the substrate is clad with a FeCrAlY metallic alloy foilhaving a nominal composition in the range from about 15 percent to about25 percent chromium, from about 3 percent to about 6 percent aluminum,from about 0.1 percent to about 1 percent yttrium. I

7. A method of protecting the surface of a substrate as claimed in claim6 wherein the substrate is clad with a FeCrAlY metallic alloy foilhaving a nominal composition of about 25 percent chromium, about 4percent aluminum, about 1 percent yttrium, and the remainder iron.

8. A method of protecting the surface of a superalloy substrate asclaimed in claim 1 wherein the metallic alloy foil is applied to thesurface of the substrate by solid state bonding.

9. A method of protecting the surface of a substrate as claimed in claim1 wherein foil cladding is applied by hot isostatic gas pressurebonding.

10. A method of protecting the surface of a superalloy substrate asclaimed in claim 1 wherein the outer aluminide coating is applied bypack cementation in ar-

1. A METHOD OF PROTECTING THE SURFACE OF A SUBSTRATE OF A METALLIC BASESYSTEM SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALTCOMPRISING THE STEPS OF CLADDING SAID SURFACE WITH A DUCTILE, OXIDATIONRESISTANT METALIC ALLOY FOIL, AND ALUMINIZING THE OUTERMOST SURFACEPORTION OF SAID FOIL THEREBY FORMING AN OUTER ALUMINIDE CONTAININGTHEREON.
 2. A method of protecting the surface of a substrate as claimedin claim 1 wherein the substrate comprises a nickel-base materialselected from the group consisting of superalloys,dispersion-strengthened alloys, composites, and directional eUtecticalloys.
 3. A method of protecting the surface of a substrate as claimedin claim 1 wherein the substrate comprises a cobalt-base materialselected from the group consisting of superalloys,dispersion-strengthened alloys, composites, and directional eutecticalloys.
 4. A method of protecting the surface of a substrate as claimedin claim 1 wherein the substrate is clad with a NiCrAlSi metallic alloyfoil having a nominal composition in the range from about 15 percent toabout 25 percent chromium, from about 3 percent to about 6 percentaluminum, from about 0.5 percent to about 1.5 percent silicon, and theremainder nickel.
 5. A method of protecting the surface of a substrateas claimed in claim 4 wherein the substrate is clad with a NiCrAlSimetallic alloy foil having a nominal composition of about 18 percentchromium, about 4 percent aluminum, about 1 percent silicon and theremainder nickel.
 6. A method of protecting the surface of a substrateas claimed in claim 1 wherein the substrate is clad with a FeCrAlYmetallic alloy foil having a nominal composition in the range from about15 percent to about 25 percent chromium, from about 3 percent to about 6percent aluminum, from about 0.1 percent to about 1 percent yttrium. 7.A method of protecting the surface of a substrate as claimed in claim 6wherein the substrate is clad with a FeCrAlY metallic alloy foil havinga nominal composition of about 25 percent chromium, about 4 percentaluminum, about 1 percent yttrium, and the remainder iron.
 8. A methodof protecting the surface of a superalloy substrate as claimed in claim1 wherein the metallic alloy foil is applied to the surface of thesubstrate by solid state bonding.
 9. A method of protecting the surfaceof a substrate as claimed in claim 1 wherein foil cladding is applied byhot isostatic gas pressure bonding.
 10. A method of protecting thesurface of a superalloy substrate as claimed in claim 1 wherein theouter aluminide coating is applied by pack cementation in argon.